Hey, I might be able to find some info for you on that... we use a rebuilt 4E to run E6 with, and all I can say is that you need to be careful cleaning those tanks. A WL is not a Jobo...the tanks have glass heating probes and thermostats in them, and if you break one or even pump the tank too low, you've pretty much ruined them. They ain't cheap--I won't elaborate, but been there/done that-- WL was owned by PSI, although I think someone else is handling them now--at any rate, they used to have this great website, with tech newsletters & such, but the current site doesn't show that stuff....I'd say to contact them for help. There are alot of those machines still in use, and there are also alot of independent shops that service them....about the worst problem with the model 4 and 4Es is that the cabinets are made of formica & , so if they get cracked & wet, they tend to fall apart. The rebuilt ones have a cabinet like the newer model 5s, but only cost about half as much or less.
The tanks are 1 and 1/3 gallons or 5 gallons. There's a line on the bottom that indicates the lowest fill level you can safely run at without cracking the heaters. The line at the top is the max fill level--you don't to go over or under these levels. I'd probably fill it up with water & try to soak them out, before getting too carried away. You'll need the nitrogen tank though to pump the water through. What processes are you planning on running?
Just don't do that gravel thing---I'd like to see you pick up the machine & vigorously shake it though, what, it's about the size of a refrigerator?